Noise is the addition of unwanted grain or splotches of color in digital photographs. It can occur by using a high ISO, such as 6400, or using very long shutter speeds that last into the minutes. In some cases, noise is a necessary evil that we need to accept, while in others, we should do everything possible to avoid it. As night photographers, we need to understand the limits of our cameras and the effects of pushing them too far.
Above photograph © Tim Cooper, via NPAN
As you may have guessed from experience with your camera’s settings, there are two types of noise: High ISO Noise and Long-Exposure Noise. Both are exactly what they sound like.
National Parks at Night is a photo workshop program focused on teaching night photography in national parks and other beautiful preserved landscapes. The diverse team of educators includes respected photographers and authors Gabriel Biderman, Tim Cooper, Matt Hill, Lance Keimig, and Chris Nicholson.
High ISO Noise
High ISO Noise appears when using a very high ISO, such as 1600, 3200, 6400 or 12800, depending on the camera being used. It makes one’s images look as though they were printed on sandpaper, as seen in the image below.
The general photographic rule of thumb is to keep your ISO as low as possible to make the shot. However, in some types of night photography (such as star points or the Milky Way), the lowest ISO possible may be 3200 or 6400. Noise-reduction tools in Adobe Lightroom and other software can help alleviate some noise, but removing it entirely often causes a softening of the image. This means we must accept some High ISO noise in certain types of images.
To determine the level of High ISO Noise you are comfortable with, simply shoot the same scene at various ISOs ranging from the lowest numerical ISO (not L -1 or L -.7) to the highest ISO your camera offers. Load them into your image editing program and examine them at 1:1 (Life-Size/100% magnification/Actual Pixels). Use your lowest ISO as a benchmark.
Long-Exposure Noise
Long-Exposure Noise is a different animal altogether. This occurs when the sensor heats up during especially long exposures—that is, long shutter speeds. This type of noise appears as splotches of color throughout the entire image, as seen in the image below, which was exposed for more than an hour.
Long-Exposure Noise is virtually impossible to fix in post-processing. The best solution is to avoid it altogether. This doesn’t mean you can’t shoot long exposures, just that you have to set your camera properly first.
Most cameras come with a function called Long Exposure Noise Reduction (LENR). Check the camera manual to find its location in the menu of your model. When LENR is engaged, it will multiply your shooting time by two. This means if your shutter is 30 seconds, your camera will shoot for 30 seconds and then for the next 30 seconds it will be busy removing any noise that may be present.
LENR typically works very well. If your camera has an Auto LENR feature, it will usually kick in after a 1-second exposure. The only drawback to using LENR is the amount of down time during which you can’t make more photographs. For this reason, it’s important to know when your camera begins to experience Long-Exposure Noise.
To begin, know that Long-Exposure Noise is exacerbated by high temperatures. You will see more of this type of noise when shooting on an 85oF night in the desert than you will when shooting in the middle of winter. For this reason, it’s a good idea to test under typical conditions. I tested my camera inside my home with the temperature set to 70oF.
Testing for Long-Exposure Noise is an important and easy step to knowing the limits of your camera. Simply set your camera up on a tripod in a dim location and begin to lengthen the time of exposure. You may want to start at 1 or 2 seconds for a benchmark image. From there, continue to use longer and longer shutter speeds until you’re unable to create a properly exposed image. Using a Polarizing Filter, Neutral Density Filter, or Variable Neutral Density Filter to block light will allow exposures into minutes.
Once you’ve made the series of images, load them onto the computer and compare them at 1:1. Knowing your long-exposure limit will allow you the most flexibility when shooting at night!
National Parks at Night's upcoming workshop locations include Joshua Tree, in California, and Cuyahoga Valley, in Ohio. To grab one of the few remaining spots, visit National Parks at Night.
1 Comment
For Sony: High ISO Noise reduction is for Jpeg only, Long Exposure Noise reduction (1" or greater) for RAW. And also that bulb 31" or longer noise that will reduce the number of stars (if you are a pixel peper). Also a hard to find option before doing night shots or those long shots wanting to get those milky water flow shots with ND filters, Reset your camera date up or back one or two months turn off (wait for the red SD card light to go out) then remove battery for 1, but 2 minutes better, replace battery and reset camera to correct date and time, again turn off camera and remove battery then replace after 2 minutes. WHY YOU MAY ASK!!! This will remap your pixels good to bad and get rid of hot (maybe) and dead pixes. This will save a trip to the factory for what you think is a repair and costly and without camera maybe a month. Lr and Capture One Pro do a good job of reducing white (dead) and red (hot) pixels upon import. Turn off all in camera noise reduction do a 1. 30 sec 2. one minute exposures low to high ISO in a dim room view on camera then in your favorite software, then do it with Noise Control on and shoot a a group of both RAW and Jpeg and then look in your favorite software. If you find camera and program will deal with higher noise than High ISO limit go to Auto ISO toggle right and adjust it up or down for that safe spot for when in Auto or P. For those who bracket for HDR there is no noise control. It took a long time to find the remapping.